Design, Synthesis, and Evaluation of Novel p-(Methylthio)styryl Substituted Quindoline Derivatives as Neuroblastoma RAS (NRAS) Repressors via Specific Stabilizing the RNA G-Quadruplex.

The human proto-oncogene neuroblastoma RAS ( NRAS) contains a guanine-rich sequence in the 5'-untranslated regions (5'-UTR) of the mRNA that could form an RNA G-quadruplex structure. This structure acts as a repressor for NRAS translation and could be a potential target for anticancer drugs. Our previous studies found an effective scaffold, the quindoline scaffold, for binding and stabilizing the DNA G-quadruplex structures. Here, on the basis of the previous studies and reported RNA-specific probes, a series of novel p-(methylthio)styryl substituted quindoline (MSQ) derivatives were designed, synthesized, and evaluated as NRAS RNA G-quadruplex ligands. Panels of experiments turned out that the introduction of p-(methylthio)styryl side chain could enhance the specific binding to the NRAS RNA G-quadruplex. One of the hits, 4a-10, showed strong stabilizing activity on the G-quadruplex and subsequently repressed NRAS's translation and inhibited tumor cells proliferation. Our finding provided a novel strategy to discover novel NRAS repressors by specifically binding to the RNA G-quadruplex in the 5'-UTR of mRNA.

Iodine-Promoted Semmler-Wolff Reactions: Step-Economic Access to meta-Substituted Primary Anilines via Aromatization.

An atom- and step-economic access to an array of unprotected meta-substituted primary anilines was disclosed using the Semmler-Wolff reaction, promoted by molecular iodine. Therein, noble metal catalysts and inert atmosphere are unnecessary while the forcing reaction conditions and the lengthy synthesis can be avoided. The synthetic utility of this approach is evident in the de novo syntheses of three bioactive molecules with good total yields.

New Disubstituted Quindoline Derivatives Inhibiting Burkitt's Lymphoma Cell Proliferation by Impeding c-MYC Transcription.

The c-MYC oncogene is overactivated during Burkitt's lymphoma pathogenesis. Targeting c-MYC to inhibit its transcriptional activity has emerged as an effective anticancer strategy. We synthesized four series of disubstituted quindoline derivatives by introducing the second cationic amino side chain and 5-N-methyl group based on a previous study of SYUIQ-5 (1) as c-MYC promoter G-quadruplex ligands. The in vitro evaluations showed that all new compounds exhibited higher stabilities and binding affinities, and most of them had better selectivity (over duplex DNA) for the c-MYC G-quadruplex compared to 1. Moreover, the new ligands prevented NM23-H2, a transcription factor, from effectively binding to the c-MYC G-quadruplex. Further studies showed that the selected ligand, 7a4, down-regulated c-MYC transcription by targeting promoter G-quadruplex and disrupting the NM23-H2/c-MYC interaction in RAJI cells. 7a4 could inhibit Burkitt's lymphoma cell proliferation through cell cycle arrest and apoptosis and suppress tumor growth in a human Burkitt's lymphoma xenograft.

Discovery of Novel 11-Triazole Substituted Benzofuro[3,2-b]quinolone Derivatives as c-myc G-Quadruplex Specific Stabilizers via Click Chemistry.

The specificity of nucleic acids' binders is crucial for developing this kind of drug, especially for novel G-quadruplexes' binders. Quindoline derivatives have been developed as G-quadruplex stabilizers with good interactive activities. In order to improve the selectivity and binding affinity of quindoline derivatives as c-myc G-quadruplex binding ligands, novel triazole containing benzofuroquinoline derivatives (T-BFQs) were designed and synthesized by using the 1,3-dipolar cycloaddition of a series of alkyne and azide building blocks. The selectivity toward c-myc G-quadruplex DNA of these novel T-BFQs was significantly improved, together with an obvious increase on binding affinity. Further cellular and in vivo experiments indicated that the T-BFQs showed inhibitory activity on tumor cells' proliferation, presumably through the down-regulation of transcription of c-myc gene. Our findings broadened the modification strategies of specific G-quadruplex stabilizers.

Discovery of Small Molecules for Repressing Cap-Independent Translation of Human Vascular Endothelial Growth Factor (hVEGF) as Novel Antitumor Agents.

Angiogenesis is important in tumorigenesis and tumor progression. Human vascular endothelial growth factor (hVEGF) is an angiogenic growth factor that plays a crucial role in tumor progression. The G-rich region within the 5'-untranslated regions (5'-UTR) of hVEGF-A mRNA can form a "switchable" RNA G-quadruplex structure that is essential for a cap-independent translation initiation. We screened our small-molecule library for binders of this G-tract. One novel quinazoline derivative, compound 1, showed a significant specific interaction with the G-tract and destabilized the G-quadruplex structure. The results of cellular experiments revealed that compound 1 down-regulated hVEGF-A translation and significantly impeded tumor cells migration. We also found that compound 1 exhibited tumor-inhibiting activity in MCF-7 xenograft tumors, which might be related to its ability to reduce hVEGF expression. These findings present a new strategy of hVEGF-A translational control in which small molecules interact with G-quadruplex structure in the 5'UTR.

Conformation Selective Antibody Enables Genome Profiling and Leads to Discovery of Parallel G-Quadruplex in Human Telomeres.

G-quadruplexes are specialized secondary structures in nucleic acids that possess significant conformational polymorphisms. The precise G-quadruplex conformations in vivo and their relevance to biological functions remain controversial and unclear, especially for telomeric G-quadruplexes. Here, we report a novel single-chain variable fragment (scFv) antibody, D1, with high binding selectivity for parallel G-quadruplexes in vitro and in vivo. Genome-wide chromatin immunoprecipitation using D1 and deep-sequencing revealed the consensus sequence for parallel G-quadruplex formation, which is characterized by G-rich sequence with a short loop size (<3 nt). By using D1, telomeric parallel G-quadruplex was identified and its formation was regulated by small molecular ligands targeting and telomere replication. Together, parallel G-quadruplex specific antibody D1 was found to be a valuable tool for determination of G-quadruplex and its conformation, which will prompt further studies on the structure of G-quadruplex and its biological implication in vivo.

Design, synthesis and biological evaluation of 4-anilinoquinazoline derivatives as new c-myc G-quadruplex ligands.

A series of 4-anilinoquinazoline derivatives were designed and synthesized as novel c-myc promoter G-quadruplex binding ligands. Subsequent biophysical and biochemical evaluation demonstrated that the introduction of aniline group at 4-position of quinazoline ring and two side chains with terminal amino group improved their binding affinity and stabilizing ability to G-quadruplex DNA. RT-PCR assay and Western blot showed that compound 7a could down-regulate transcription and expression of c-myc gene in Hela cells, which was consistent with the behavior of an effective G-quadruplex ligand targeting c-myc oncogene. More importantly, RTCA and colony formation assays indicated that 7a obviously inhibited Hela cells proliferation, without influence on normal primary cultured mouse mesangial cells. Flow cytometric assays suggested that 7a induced Hela cells to arrest in G0/G1 phase both in a time-dependent and dose-dependent manner.

Complicated behavior of G-quadruplexes and evaluating G-quadruplexes' ligands in various systems mimicking cellular circumstance.

Environments surrounding G-rich sequences remarkably affect the conformations of these structures. A proper evaluation system mimicking the crowded environment in a cell with macromolecules should be developed to perform structural and functional studies on G-quadruplexes. In this study, the topology and stability of a G-quadruplex formed by human telomeric repeat sequences were investigated in a macromolecule-crowded environment created by polyethylene glycol 200 (PEG200), tumor cell extract, and Xenopus laevis egg extract. The interactions between small molecules and telomeric G-quadruplexes were also evaluated in the different systems. The results suggested that the actual behavior of G-quadruplex structures in cells extract is quite different from that in the PEG crowding system, and proteins or other factors in extracts might play a very important role in G-quadruplex structures.

A newly identified berberine derivative induces cancer cell senescence by stabilizing endogenous G-quadruplexes and sparking a DNA damage response at the telomere region.

The guanine-rich sequences are able to fold into G-quadruplexes in living cells, making these structures promising anti-cancer drug targets. In the current study, we identified a small molecule, Ber8, from a series of 9-substituted berberine derivatives and found that it could induce acute cell growth arrest and senescence in cancer cells, but not in normal fibroblasts. Further analysis revealed that the cell growth arrest was directly associated with apparent cell cycle arrest, cell senescence, and profound DNA damage at the telomere region. Significantly, our studies also provided evidence that Ber8 could stabilize endogenous telomeric G-quadruplexes structures in cells. Ber8 could then induce the delocalization of TRF1 and POT1 from the telomere accompanied by a rapid telomere uncapping. These results provide compelling insights into direct binding of telomeric G-quadruplexes and might contribute to the development of more selective, effective anticancer drugs.

RNA G-Quadruplex: The New Potential Targets for Therapy.

Roles of RNA on transcriptional and post-transcriptional regulations have raised more attention since the new era of genomics. One of the secondary structures of RNA, the RNA Gquadruplex structure, is demonstrated a relatively stable existence in human tumor cells, virus, or other species relating to diseases. G-quadruplexes are special secondary structures formed by G-rich DNA and RNA sequences that fold into a four-stranded conformation. The G-quadruplexes formed in RNA are involved in many biological process including telomere elongation, transcription regulate, pre-mRNA splicing and translation. In this review, we will give a brief introduction to the structures of RNA G-quadruplexes, the biological roles and the potential to be as drug targets.

Dissipative soliton resonance in a passively mode-locked figure-eight fiber laser.

The generation of mode-locked rectangular pulses operating in dissipative soliton resonance (DSR) region is demonstrated in an erbium-doped figure-eight fiber laser with net anomalous dispersion. The duration of the wave-breaking-free rectangular pulse broadens with the increase of pump power. At a maximum pump power of 341 mW, the pulse energy can be up to 3.25 nJ with a repetition rate of 3.54 MHz. Particularly, the spectrum of rectangular pulse operating in DSR exhibits conventional soliton sidebands. The observed results show that the formation of pulse operating in DSR region is independent of mode-locking techniques, which may be helpful for further understanding the DSR phenomenon.